JP2000015176A - Organically coated galvanized steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organically coated galvanized steel sheet excellent in corrosion resistance (white rust resistance) and adhesion by single-layer treatment other than chromate treatment. SOLUTION: A dry coating film of an aq. soln. contg. 100 pts.wt.aq. colloidal silica having <=10 nm particle diameter and not subjected to dispersion stabilization with alkali metal actions and 100-1,000 pts.wt. water-soluble resin having <=100 nm particle diameter and not contg. a free emulsifier is formed on a galvanized steel sheet by 0.5-2.0 g/m2 to obtain the objective organically coated galvanized steel sheet. The aq. colloidal silica is preferably subjected to dispersion stabilization with ammonium ions and the water-soluble resin is preferably synthesized using a reactive emulsifier and contains an acrylic resin contg. one or more of silanol, hydroxyl, glycidyl and phosphoric acid groups as an essential component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet mainly used for home appliances, which does not contain any harmful hexavalent chromium on the steel sheet and which is used in a manufacturing process.
The present invention relates to a galvanized steel sheet which has no emission of chromium (VI) and has the same corrosion resistance and paint adhesion as a conventional chromate-treated steel sheet containing hexavalent chromium.

[0002]

2. Description of the Related Art Zinc-based plated steel sheets are widely used as steel sheets for home appliances, building materials and automobiles from the viewpoint of corrosion resistance.
However, zinc alone is not sufficient in terms of corrosion resistance and the appearance deteriorates due to the generation of white rust.In addition, when used as a coating base, adhesion to paint cannot be ensured, so chromate treatment and zinc phosphate treatment are usually used. Done. In the case of the chromate treatment, the function of suppressing white rust is great, but the adhesion to the paint is not always sufficient. In addition, there is a problem that a large amount of harmful hexavalent chromium is contained. On the other hand, in the case of zinc phosphate treatment, the adhesion with the paint is relatively good, but the white rust suppression function when used naked is extremely weak,
Therefore, the sealing treatment is performed with a treatment liquid containing harmful hexavalent chromium as in the case of the normal chromate treatment. A steel sheet in which a chromate layer is formed as a first layer on a zinc-based plating, and an organic coating is further provided on the chromate layer is also known. in this case,
Although there is no elution of hexavalent chromium, the content is not zero due to the chromate treatment. Further, in the manufacturing process, hexavalent chromium is inevitably discharged, so it is still environmentally unfavorable. . To solve these problems, it has been proposed to dispose the chromate layer and provide an organic coating layer directly on the galvanized layer. For example, JP
JP-A-92846 proposes formation of an organic-inorganic composite film of an organic resin, a silane coupling agent, and silica. Japanese Patent Application Laid-Open No. 6-316686 proposes forming a film directly on zinc plating with fine particles of a copolymer of methyl methacrylate, styrene and a crosslinkable monomer. Japanese Patent Application Laid-Open No. Hei 9-221595 proposes a treatment on galvanization using a carbodiimide bond-containing resin. Japanese Patent Application Laid-Open No. 8-6783
No. 4, No. 8-239776, No. 8-267004
Japanese Patent Application Publication No. JP-A-2002-115,086 discloses a rust-preventive composition on zinc plating containing an aqueous resin and an S or P compound as a rust-preventive agent. In each of the above examples, a relatively good corrosion resistance can be ensured by increasing the film thickness.However, when trying to obtain the same corrosion resistance as that of the chromate treatment, the film thickness becomes extremely thick, which is uneconomical. At the same time, problems such as welding and processing also occur. Furthermore, when used as a coating base, the adhesion between the top coat is good, but since there is no chromate layer or zinc phosphate layer that mediates the adhesion between the zinc and the film, the There is a problem that the adhesion is extremely poor, and in particular, the water-resistant adhesion cannot be secured at all. Japanese Patent Application Laid-Open No. 5-200357 discloses a method of forming a resin coating film made of a two-component reaction type epoxy resin containing an epoxy-based silane coupling agent on zinc plating. The adhesion between the resin coatings in a water-resistant environment is not sufficient, and a thick film of about 80 μm is required to ensure corrosion resistance. Such a thick film has problems in weldability and workability, and is unsuitable as a general-purpose steel sheet for home appliances. In the case of zinc, the affinity of the metal surface with water and oxygen is greater than in the case of metals such as iron,
Even if the resin is brought into close contact with the zinc surface, it is considered that, for example, in a water-resistant environment, the dissociative adsorption bond of water easily replaces the bond between zinc and the resin, so that it is difficult to secure the adhesion. In order to solve this problem, for example, Japanese Patent Application Laid-Open No. 58-98248 discloses a method in which a lithium silicate layer is formed on a galvanized layer and an organic-inorganic composite film is further formed thereon.
Even in this case, the performance is not always sufficient, and the processing is performed in two layers, which is disadvantageous in cost and process.

[0003]

According to the present invention, there is provided an organic-coated galvanized steel sheet which is excellent in corrosion resistance (white rust resistance) and adhesion by treating one layer without chromate treatment. The purpose is to:

[0004]

The gist of the present invention is as follows: (1) The particle size of the electrogalvanized steel sheet is 10 nm or less,
And 100 parts by weight of aqueous colloidal silica not subjected to the dispersion stabilizing effect of alkali metal cations, and a dried film of an aqueous solution containing 100 to 1000 parts by weight of an aqueous resin having a particle size of 100 nm or less and containing no free emulsifier. 0.
Featuring a 5 to 2.0 g / m ² formed was that, organic coated galvanized steel. (2) The organic-coated galvanized steel sheet according to the preceding paragraph, wherein the aqueous colloidal silica has been subjected to a dispersion stabilizing action by ammonium ions. (3) The organic-coated galvanized steel sheet according to the preceding paragraph, wherein the aqueous resin is synthesized using a reactive emulsifier. (4) The organic-coated galvanized steel sheet as described in the preceding item, wherein the aqueous resin contains, as an essential component, an acrylic resin containing one or more of a silanol group, a hydroxyl group, a glycidyl group, and a phosphate group. It is.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described in the prior art, if an ordinary organic coating treatment is performed directly without forming a chromate layer or a zinc phosphate layer on zinc, the adhesion in a water-resistant environment is reduced. As a result, no satisfactory corrosion resistance can be obtained. As a result of repeated studies to solve this problem, impurities contained in trace amounts of silica and aqueous resin are the main causes of performance degradation, and after excluding these, specific aqueous silica and specific aqueous resin have a specific ratio. As a result, they found that applying them on a specific galvanized steel sheet could solve the problem.

Here, the silica must be an aqueous colloidal silica, and a dry silica (fumed silica) or a solvent-based silica dispersion cannot provide any desired performance. This is presumed to be due to the fact that aqueous colloidal silica has many OH groups on the surface, and this has some effect on the zinc surface. Further, it is essential that the particle size of the colloidal silica be 10 nm or less. Further, the colloidal silica which has been subjected to a dispersion stabilizing action by an alkali metal cation such as Na, K, Li or the like cannot be used because it inhibits the water resistance and adhesion of the formed film. As the colloidal silica, those stabilized by ammonium ions or pure colloidal silicate can be used. In this case, good adhesion is obtained. In particular, from the viewpoint of adhesion, those stabilized by ammonium ions are preferable. Next, for the aqueous resin, it is first essential not to include a free emulsifier. Usually, a method of synthesizing an aqueous resin composition in which an emulsifier is added to a synthesized resin, followed by mechanical stirring and dispersion in water is often employed. The aqueous resin produced in this manner leaves a large amount of emulsifier in the dried film, and has poor water resistance,
Corrosion also proceeds easily. Also, the adhesion to zinc is poor. As a method of synthesizing an aqueous resin other than the dispersion using an emulsifier, for example, a method of synthesizing an acid group-containing polymer such as a carboxyl group or a sulfonic acid group, and then neutralizing the acid group portion with an amine or the like to disperse in water. A method of synthesizing an amine group-containing polymer, neutralizing the amine group with an acid or the like, and dispersing in water.
Examples include a method of synthesizing a polymer in water using a reactive emulsifier.In particular, a method using a reactive emulsifier includes not only an emulsifier in a film but also an organic solvent or the like that could not be removed in the synthesis process. And most preferred. In addition,
As a natural consequence of the fact that aqueous colloidal silica is essential as a silica source, a solvent-based resin composition has a problem with miscibility with colloidal silica and cannot be used. It is essential that the particle size of the aqueous resin is 100 nm or less.
It is presumed that the corrosion resistance is poor and the formed film becomes coarse. The solid content weight ratio of the above-mentioned colloidal silica and the aqueous resin is as follows.
It needs to be in the range of 0 to 1000, preferably 250 to 500. If the weight ratio of the resin is lower than this range, a problem occurs in the formation of the film, and the corrosion resistance deteriorates. In addition, the adhesiveness when an impact is applied also deteriorates. If the weight ratio of the resin is larger than a predetermined value, adhesion to zinc, particularly in a water-resistant environment cannot be secured at all, and corrosion resistance is poor.

As the type of the water-based resin, any of an acrylic resin, an epoxy resin, a urethane resin and the like can be used. From the viewpoints of corrosion resistance and adhesion, acrylic resins, acrylic / olefin resins, and acrylic resins are more preferable. It is a resin containing an acrylic component such as a styrene type, an acrylic / urethane type, and an acrylic / epoxy type. Further, in this acrylic component, a silanol group, a hydroxyl group, a glycidyl group,
It is desirable to contain a reactive group such as a phosphate group, and these groups may be used alone or in combination of two or more.

It is necessary to apply the above-mentioned composition of colloidal silica and water-based resin on an electrogalvanized steel sheet. For example, when the composition is treated on hot-dip galvanized steel, a predetermined performance cannot be obtained. The method of application is not particularly limited, such as spraying or roll coating, but application by roll coating is preferred from the viewpoint of the finished appearance and the controllability of the applied thickness.
Drying after application may be performed as long as water can evaporate.
More preferably, the steel sheet is heated for several seconds to several minutes so that the steel sheet temperature becomes about 100 to 200 ° C. The film weight after drying is 0.5 to ² g / m ² , and if it is less than 0.5,
If the corrosion resistance is insufficient, and if it is ² g / m ² or more, the effect of the corrosion resistance is saturated, which is not only uneconomical, but also may cause failure in welding applications, which is not preferable.

[0009]

Examples of the present invention will be described below.

(Example 1) An electrogalvanized steel sheet (sheet thickness 0.7 mm, basis weight) was used as a sample adjustment base material.
(20 g / m ² / one side), after alkali spray degreasing, various treatment liquids were applied by a roll coater, and immediately thereafter, heated in a hot-air drying oven for several seconds at a sheet temperature of 100 ° C. and allowed to cool.
In addition, in some comparative examples, the hot-dip galvanized steel sheet (0.7 m
m, and a basis weight of 60 g / m ² / one side). The treatment liquid used was a mixture of various parts by weight of an aqueous resin with respect to 100 parts by weight of various silicas. Here, the aqueous resin was synthesized using an anionic reactive emulsifier,
MMA (methyl methacrylate) containing glycidyl group /
An aqueous dispersion of a styrene resin (particle size: 60 nm) was used. Further, as a comparative material, those subjected to electrolytic chromate treatment to the same electro-galvanized steel sheet (Cr20mg / m ^2), also coated chromate (38% reduction chromic acid + silica treatment liquid is applied,
Drying at 100 ° C. and Cr50 mg / m ² ) was also used.

Evaluation method "Nude corrosion resistance" After processing a flat plate and Erichsen 7 mm (in each case, a tape seal on the edge and the back surface), JI
By the salt spray test of SZ-2371, the area ratio of white rust and total discoloration after 10 days was measured. (Xx; 100%, x;
80-99%, △; 50-79%, ○: 20-49%, ◎; 1-20%
, ◎◎; 0%) "Adhesion" Kansai Paint Amirac # 1000 coated with 20μ, (Primary adhesion) 1mm cross-cut tape peeled, (Secondary adhesion) Boiling water immersed for 30 minutes, 50 ° C hot water 3 Sun immersion, 1mm cross-cut tape peeling, and after 1mm cross-cut, extruded 7mm of Erichsen and peeled the tape. Evaluated by peeling area ratio. (Xx; 10
0%, ×: 80 to 99%, Δ: 50 to 79%, ○: 20 to 49%, ；;
The results are shown in Table 1. In the examples of the present invention, the corrosion resistance and paint adhesion are all superior to or higher than those of conventional chromate-treated steel sheets. Anything out of the box had some performance degradation.

[0012]

[Table 1]

(Example 2) Sample preparation The same base material as in Example 1 was treated in the same manner. The coating liquid used here was a mixture of 350 parts by weight of various aqueous resins with respect to 100 parts by weight of ammonia-stable colloidal silica having a particle size of 5 nm. Acrylic resin is a resin mainly composed of MMA, and urethane is a polyester type polyurethane. All dry film weight is 1.0g
/ was m ^2.

Evaluation method The evaluation method is the same as in the first embodiment. Table 2 shows the results. In the examples of the present invention, both the corrosion resistance and the paint adhesion were excellent, but those deviating from the conditions stipulated in the present invention deteriorated some performance.

[0015]

[Table 2]

[0016]

According to the present invention, an organic-coated galvanized steel sheet having excellent corrosion resistance (white rust resistance) and adhesion is provided by one-layer organic treatment without chromate treatment. This indicates that the performance of the conventional chromate-treated galvanized steel sheet could be replaced without containing harmful components,
The significance is great. In addition, since it is an organic coating treatment, it is excellent in fingerprints and workability compared to chromate treatment,
By compounding various additives in the organic coating, various functional requirements can be easily met.

Continued on the front page F term (reference) 4D075 BB24Z BB87X BB92Z CA13 CA33 DB02 DB05 EA06 EA12 EA13 EB14 EB22 EB56 EB57 EC03 EC31 EC53 EC54

Claims (4)

[Claims] 1. An electrogalvanized steel sheet having a particle size of 10
aqueous colloidal silica having a particle size of 100 nm or less and a free emulsifier-free aqueous resin having a particle size of 100 nm or less and an aqueous resin having a particle size of 100 nm or less and having not been subjected to the dispersion stabilizing effect of the alkali metal cation. featuring that the dry coating was 0.5 to 2.0 g / m ² formed, the organic coating galvanized steel sheets. 2. The organic-coated galvanized steel sheet according to claim 1, wherein the aqueous colloidal silica has been subjected to a dispersion stabilizing action by ammonium ions. 3. The organic-coated galvanized steel sheet according to claim 1, wherein the aqueous resin is synthesized using a reactive emulsifier. 4. The organic material according to claim 1, wherein the aqueous resin contains an acrylic resin containing one or more of a silanol group, a hydroxyl group, a glycidyl group and a phosphate group as an essential component. Coated galvanized steel sheet.